The present invention relates to an integrated electrically actuated mechanical release mechanism, and more particularly to such a mechanism when used as part of an electrical safety device such as a residual current circuit breaker.
Various mechanisms are known in the art which provide electrical safety protection from a variety of potential electrical faults. Unfortunately each mechanism is usually designed to provide protection from a particular type of electrical fault. Various relevant types of electrical fault which may occur are, for example, a gross over-current condition such as may occur with a short circuit, an unbalanced fault current condition in the connections leading to and from the electrical supply, or a small fault current which, although insufficient to trip any short circuit protective mechanism, may still be damaging to sensitive electronic components in any device to which the safety mechanism is applied. Typically, a separate detection and actuation mechanism has previously been required for each type of fault, meaning that electrical safety could only be guaranteed within particular electrical regimes.
It is an object of the present invention to provide an integrated unitary electrically actuated release mechanism which integrates multiple level electrical protection into a single system.
In order to meet the above object, the present invention provides a integrated electrically actuable mechanical release mechanism comprising first fault detection means arranged to detect a first fault condition in an electric circuit; second fault detection means arranged to detect a second fault condition in the electrical circuit; third fault detection means arranged to detect a third fault condition in the electrical circuit; and means for breaking the electrical circuit in response to detection of any of the first, second or third fault conditions.
The first fault condition is preferably a low fault current condition which is insufficient to trip a short-circuit protection mechanism. The second fault current condition may preferably be a current imbalance between two or more parts of a circuit. The third fault current condition may preferably be a gross over-current condition such as those associated with a short-circuit condition.
In a preferred embodiment, the first fault detection means preferably comprises a bimetallic strip arranged to bend in response to the occurrence of the first fault condition in the circuit. Furthermore, the second fault detection means preferably includes an active material bender arranged to bend in response to the occurrence of the second fault condition. Moreover, in the preferred embodiment the third fault detection means preferably comprises a coil wound around a core, the core being ejected from within the coil on the occurrence of the third fault condition.
Preferably, the active material bender is a piezo active material bender as disclosed in our earlier international application no WO-A-98/40917, the relevant features of which necessary for a full understanding of the present invention being incorporated herein by reference.
The active material bender may by manufactured from a plurality of laminar members which are stacked one on top of the other to produce a low profile device.
A drive circuit is further provided for the active material bender which includes a toroidal transformer having primary and secondary coils arranged thereon adapted to detect current imbalances in two or more parts of the electrical circuit. The transformer is preferably further arranged to saturate at a level of current imbalance less that indicative of a second fault condition, the saturation of the core resulting in a high-voltage low-power output drive signal which can be used to drive the active material bender.
All of the detection means (the bimetallic member, the active material bender, and the coil) are preferably line independent, in that the energy of the fault current is used to actuate the detection means. Furthermore, all the faults to be detected are preferably current-driven.
The present invention has a primary advantage in that it provides an integrated unitary actuator which provides electrical protection from a variety of different electrical faults. Electrical safety can therefore be maintained over a wide range of electrical operating conditions.